The present invention relates generally to grinding machines having a cylindrical grinding wheel mounted on a vertical shaft extending through a horizontal work surface. More particularly, the present invention relates to such grinding machines having an improved work table and grinding wheels.
Grinding machines of the type disclosed herein are typically used for grinding certain work pieces to a particular shape, including, but not limited to, glass, ceramic tile, stone, marble, fiberglass and plastic work pieces. Primarily, the work piece is a piece of stained glass for making stained glass windows. When the work piece is to be ground, the work piece is placed on a work table and manually applied to a grinding wheel that is rotated by an electric motor. Power to the motor is switched on and off during periods of use and non-use of the machine by means of hand or foot operated switches. While these switches are functional, they sometimes distract one's eyes from the work piece. Also, a machine operator may leave the switch on when the machine is not in use resulting in an unsafe condition, and reducing the useful life of the grinding machine. It would be desirable to have a more convenient and efficient means for activating and deactivating the motor.
During the operation of a grinding a particular work piece, it is often necessary to change the grinding wheel, for example, to a grinding wheel having a different abrasive grit or abrasive characteristic, or to replace a grinding wheel which has been worn out. Grinding wheels are generally coaxially mounted on a vertical shaft driven by the electric motor and secured in place by means of a set screw or the like. Replacement of the grinding wheel simply involves loosening of the set screw, removing the old wheel, mounting the new wheel and then tightening the set screw on the new wheel. This procedure, while straight forward, is sometimes difficult or unpleasant because of ground glass or other material that has solidified in the area of the set screw. Further, replacement of the entire grinding wheel can be somewhat costly because the entire grinding wheel needs to be replaced as opposed to just replacing the abrasive grinding portion of the grinding wheel. In addition, because the cost of replacing the abrasive grit portions would be lower than replacing the entire grinding wheel, a user could afford a larger variety of sizes and profiles of wheels. Thus, it would be desirable to have a grinding wheel assembly which facilitates changing grinding wheels in which an abrasive grit portion of the grinding wheel was replaced and a remaining core portion of the grinding wheel was reused.
The grinding machines of the type described herein are used to grind work pieces having a wide variety of shapes and sizes. For most commonly used sizes of work pieces a regular sized work table is sufficiently large to support the work piece. However, for large work pieces it would be desirable if an oversized work table were available to be substituted for the regular work table.
The grinding wheels used in association with the grinding machines of the type described herein come in a variety of wheel diameters. Those grinding wheels where the abrasive grit portion is on a side of the grinding wheel have generally been limited to no greater than one inch in diameter because it has heretofore been thought that grinding wheels of a greater diameter having grit portions on the side surface would cause the motor rotating the grinding wheel to bog down during the grinding process. Larger grinding wheels are, however, known in the art, some having diameters of up to six inches, for the type of grinding machines described herein, but the abrasive grit portion of these wheels has been limited to only a top surface of the grinding wheel. In this configuration, the grinding pressure of a workpiece applied to the grinding wheel is in a direction substantially parallel to the shaft of the motor, and therefore the motor would generally not bog down. However, because a larger diameter grinding wheel would provide a greater outside diameter speed for the same motor speed, the grinding rate of such a wheel would be significantly increased. It would therefore be an advantage to have a relatively larger diameter grinding wheel that allowed grinding on a side contoured surface of the grinding wheel, and did not cause the motor to bog down during the grinding process. It would further be an advantage to provide a grinding machine that included a large grinding wheel that allowed grinding on a top surface and a side surface of the wheel and a smaller diameter grinding wheel on the same motor shaft.
The grinding machine of the type described herein generally includes a reservoir beneath the work table of the grinding machine that holds a cooling fluid that acts to cool the grinding wheel and work piece during the process of grinding. Due to evaporation, splashing, and other factors, the cooling fluid is reduced over time to levels that are unacceptable for cooling purposes. Therefore, the reservoir needs to be periodically refilled with new cooling fluid. Because the work table is generally a grate structure, it is applicable to allow the cooling fluid to be poured through the work table into the reservoir. However, a problem exists in that it is not always apparent what the level of cooling fluid is in the reservoir. Therefore, when replacing the cooling fluid, the cooling fluid may overflow the reservoir, or the reservoir may not receive enough cooling fluid. It therefore would be desirable to provide some kind of level indicator of the cooling fluid within the reservoir.
With the above points in mind, we have invented a new and improved grinding apparatus. Accordingly, the apparatus of the present invention has a touch-top work table which enables an operator to turn on the motor by applying slight downward force pressure on the table and to turn off the motor by releasing the downward force on the work table. Also, the work table of the present invention can be easily interchanged with other work tables. Furthermore, the grinding wheel of the present invention facilitates removal of old wheels and installation of new wheels without having to remove the core of the grinding wheel that is secured to the shaft of the electrical motor. Further, a coolant level indicator is provided that provides an indication of cooling fluid in the reservoir.
Further understanding of the present invention will be had from the following detailed description and claims taken in conjunction with the accompanying drawings.